Cigarette smoking and chronic allograft nephropathy

NDT Advance Access published May 21, 2007 Nephrol Dial Transplant (2007) 1 of 6 doi:10.1093/ndt/gfm275

Original Article

Cigarette smoking and chronic allograft nephropathy Nina Zitt1,2, Barbara Kollerits3, Ulrich Neyer2, Walter Mark4, Dorothea Heininger1, Gert Mayer1, Florian Kronenberg3 and Karl Lhotta1 1

Clinical Division of Nephrology, Innsbruck Medical University, Innsbruck, 2Department of Nephrology and Dialysis, Academic Teaching Hospital Feldkirch, Feldkirch, 3Division of Genetic Epidemiology, Department of Medical Genetics, Molecular and Clinical Pharmacology and 4Clinical Division of Transplant Surgery, Innsbruck Medical University, Innsbruck, Austria

Correspondence and offprint request to: Dr Karl Lhotta, Clinical Division of Nephrology, Innsbruck Medical University, Anichstrasse 35, A-6020 Innsbruck, Austria, Email: [email protected]

current smoking (P ¼ 0.004), whereas the degree of arteriolar hyalinosis (P < 0.001) and chronic/sclerosing nephropathy (P ¼ 0.05) were associated with time since transplantation. Conclusions. The number of patients who continue cigarette smoking after renal transplantation has decreased in recent years. The main allograft lesion associated with smoking is fibrous intimal thickening of small arteries. Keywords: arteriolar hyalinosis; arteriopathy; cigarette smoking; chronic allograft nephropathy; kidney transplantation

Introduction Chronic allograft nephropathy has become the leading cause of late kidney transplant failure [1]. Its histological hallmarks are tubular atrophy, interstitial fibrosis, microvascular changes and glomerulosclerosis [2]. The prevalence and severity of chronic allograft pathology increase with time elapsed after transplantation [3,4]. Chronic allograft nephropathy is driven by a number of immunological and non-immunological factors such as pre-existing donor pathology, ischaemia reperfusion injury, acute tubular necrosis, acute rejection, hypertension or calcineurin inhibitor toxicity (reviewed in [5]). Cigarette smoking has been identified as a progression factor in various kidney diseases, for example, diabetic nephropathy [6], hypertensive kidney disease [7], lupus nephritis [8], IgA nephropathy and autosomal dominant polycystic kidney disease [9]. Because progression factors of native kidney disease usually also aggravate chronic allograft nephropathy, we hypothesized that this is also the case for cigarette smoking. The present study was undertaken to investigate any potential impact of smoking on both function of and morphological changes in renal allografts.

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Abstract Background. Smoking has been demonstrated to decrease patient and graft survival after kidney transplantation. Data on histological changes associated with smoking in renal allografts are lacking. Methods. Smoking habits before and after renal transplantation were evaluated by questionnaire in 279 patients. A transplant biopsy was performed more than 1 year after transplantation in 76 of them. Histological changes were classified according to Banff 97 criteria. Linear regression analysis and proportional odds models for histological changes including the factors age, gender, diabetes, body mass index, donor age, time since transplantation, history of acute rejection and smoking status were calculated. Results. Overall 22% of patients continued smoking after transplantation, with the proportion decreasing from 38% of those transplanted before 1990 to 13% of those transplanted after 2000. Serum creatinine was non-significantly higher in smokers (2.3 2.7 mg/dl vs 1.8 1.4 mg/dl, P ¼ 0.21). A renal biopsy was performed in 24% of non-smokers and 39% of smokers (P ¼ 0.02), and smokers were biopsied on average 1.5 years earlier. Among biopsied patients current smokers tended to suffer more often from diabetes (25.0% vs 13.5%, P ¼ 0.33), to develop transplant failure (33.3% vs 21.2%, P ¼ 0.25) or experience a cardiovascular event (29.2% vs 15.4%, P ¼ 0.16). The frequency of acute rejection was comparable between smokers and non-smokers (25.0% vs 34.6%, P ¼ 0.40). Glomerular sclerosis was associated with diabetes (P ¼ 0.03). Severity of vascular intimal fibrous thickening was associated with

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Results

Patients

Smoking habits of patients

All 272 prevalent transplant patients older than 18 years with a functioning kidney allograft and under regular control at the Nephrology Departments in Innsbruck and Feldkirch were included in the study. In addition, seven patients who had been included in the renal biopsy study (see further) but were back on dialysis were also enrolled. Patients under investigation had undergone kidney transplantation between 1974 and 2004. The investigation was performed during the summer of 2005. After informed consent was obtained, patients were asked to fill out a questionnaire about their smoking habits during a control visit at the out-patient department. They were asked in detail whether they were non-smokers, ex-smokers or current smokers. Smokers were asked the number of cigarettes per day and the years of smoking before and after transplantation. In addition, exsmokers were asked when they quit smoking. Current laboratory parameters as well as age, height, weight, blood pressure, immunosuppressive medication and other therapies were determined from the patient chart. Patients were classified as having experienced an acute rejection episode if this was confirmed by transplant biopsy or if it was clinically diagnosed and followed by anti-rejection therapy.

In total 279 prevalent patients at the two participating units were included in this study. Overall 62 (22%) patients continued smoking after transplantation, 106 (38%) were ex-smokers (that means they quit prior to or at the time of transplantation), and 111 (40%) patients never smoked. The percentage of patients who continued smoking decreased with the time when transplantation was performed. Of those transplanted before 1990, 11 (38%) continued smoking, of those transplanted between 1990 and 1999, 36 (26%) continued, and the proportion of smokers further decreased to 13% (n ¼ 15) in those transplanted after 2000. This decrease was paralleled by an increase in patients who quit smoking before or at the time of transplantation. The proportion of non-smokers remained constant over time. The number of pack years smoked before transplantation was identical for ex-smokers (18.6 17.2) and current smokers (18.2 17.0). Current smokers had smoked 4.0 4.1 pack-years since renal transplantation. The clinical and laboratory data of all 279 patients with further stratification for current smokers and non/ex-smokers are shown in Table 1. Current smokers were younger, had higher triglyceride levels and a lower body mass index. Smokers tended to have higher serum creatinine levels. This trend towards higher serum creatinine in smokers was also observed after stratification for gender and for transplantation before 1990, between 1990 and 2000, and after 2000, however, without being significant in any subgroup. The time elapsed since transplantation was longer in smokers. This was reflected in a shift in immunosuppression from azathioprine to mycophenolic acid and in a higher proportion of non-smokers treated with tacrolimus. Target trough levels within the first year were 150–200 ng/ml for cyclosporin A and 8–12 ng/ml for tacrolimus, and thereafter 80–120 ng/ml for cyclosporin A and 5–8 ng/ml for tacrolimus. A transplant biopsy was more often performed in smokers than in non-smokers (39% vs 24%, P ¼ 0.02). Smokers with biopsy had smoked 3.1 4.0 pack-years from transplantation until biopsy.

Renal biopsies Biopsies performed at least 1 year after transplantation were evaluated. All biopsies were done at the discretion of the treating physician. Relevant laboratory variables and immunosuppressive treatment at the time of biopsy were retrieved from patient charts. According to the Banff 97 working classification of renal allograft pathology, chronic/sclerosing allograft nephropathy was graded as mild, moderate or severe. In addition, quantitative criteria for vascular fibrous intimal thickening and arteriolar hyaline thickening were determined as described in the Banff 97 classification [2]. The study protocol was approved by the institutional review boards of both institutions.

Statistical analysis Statistical analysis was performed with the Statistical Package for the Social Sciences (SPSS) for Windows 12.01. Univariate comparisons of continuous variables between various groups were performed using an unpaired t-test or the non-parametric Wilcoxon rank sum test for nonnormally distributed variables. Dichotomized variables were compared using Pearson’s 2 test. Differences were considered significant at P < 0.05. Data are presented as mean SD and as 25th, 50th and 75th percentile for skewed variables where appropriate. Multiple adjusted risk estimates for glomerulosclerosis were calculated using linear regression analysis. Odds ratios derived from ordinal logistic regression analysis for arteriopathy, arteriolopathy and chronic sclerosing allograft nephropathy refer to the odds of being lower or higher on the outcome variable across the entire range of the outcome. The proportional odds assumption was tested.

Evaluation of transplant biopsies All patients with a renal biopsy were further stratified into non-smokers after transplantation and current smokers (Table 2). Smokers were biopsied on average 19 months earlier than non-smokers, however, this difference was not significant (P ¼ 0.16). There was also a trend towards more cardiovascular events in smokers (29.2 vs 15.4%, P ¼ 0.16), and they tended to have diabetes more frequently (25.0% vs 13.5%, P ¼ 0.33). The proportion of patients who had experienced transplant failure by the end of 2006 was


Materials and methods

Smoking and chronic nephropathy

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Table 1. Clinical and laboratory data and immunosuppression of 279 transplant patients with further stratification into non/ex-smokers and smokers Non/ex-smokers (n ¼ 217)

Smokers (n ¼ 62)

P-value

190/89 (68.1/31.9) 51.9 13.0 25.7 4.4 18.4 17.1 [6.0;14.9;25.0] 1.9 1.8 [1.1;1.5;1.9] 51 22 66 (25.3) 137 17 83 10 195 44 119 38 61 20 166 112 [96;140;190] 76 (27.2) 127 (48.5) 87 58 [45;72;117] 63 (23.1) 192 (68.8) 75 (26.9) 9 (3.2) 102 (36.6) 132 (47.3) 262 (93.9)

146/71 (67.3/32.7) 53.5 13.1 26.0 4.6 18.6 17.2a [6.0;14.9;26.9] 1.8 1.4 [1.1;1.5;1.9] 52 22 54 (26.2) 137 17 83 10 195 43 120 36 62 19 156 90 [94;131;187] 52 (24.0) 97 (47.5) 83 57 [44;67;113] 51 (24.2) 148 (68.2) 65 (30.0) 7 (3.2) 87 (40.1) 94 (43.3) 203 (93.5)

44/18 (71.0/29.0) 46.1 11.0 24.6 3.8 18.2 17.0 [5.0;13.0;23.3] 2.3 2.7 [1.2;1.5;2.2] 49 23 12 (21.8) 138 16 84 9 195 49 116 43 59 22 201 166 [108;160;253] 24 (38.7) 30 (51.7) 101 59 [56;92;140] 12 (19.4) 44 (71.0) 10 (16.1) 2 (3.2) 15 (24.2) 38 (61.3) 59 (95.2)

0.58 4. Only few studies have investigated the impact of smoking on patient and graft survival in renal transplant recipients, and none of them included data on allograft histology. In most reports smoking status was determined only prior to or at the time


Gender (male/female), n (%) Age (years) Body mass index (kg/m2) Pack-years before transplantation Serum creatinine (mg/dl) Glomerular filtration rate (ml/min/1.73m2)b Proteinuria (mg/g), >300 mg/g, n (%)c Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Total cholesterol (mg/dl) LDL cholesterol (mg/dl) HDL cholesterol (mg/dl) Triglycerides (mg/dl) Biopsy, n (%) Donor age, above median (years), n (%)d Time since transplantation (months) Cardiovascular event, n (%)e Cyclosporin A, n (%) Tacrolimus, n (%) Sirolimus, n (%) Mycophenolic acid, n (%) Azathioprine, n (%) Steroids, n (%)

All patients (n ¼ 279)

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Table 2. Clinical and laboratory data and markers of chronic allograft nephropathy of 76 transplant patients with biopsy, with further stratification into non/ex-smokers and smokers Non/ex-smokers (n ¼ 52)

Smokers (n ¼ 24)

P-value

2.9 1.6 [1.8;2.4;3.2] 30.7 15.2

2.7 1.1 [1.8;2.4;3.2] 32.1 15.1

3.3 2.3 [2.0;2.9;3.6] 27.3 15.0

0.38 0.23

139 17 84 11 191 49 170 98 13 (17.1) 19 (26.1) 9 (11.8) 24 (31.6) 31 (43.7)

139 17 84 10 192 45 171 90 7 (13.5) 11 (21.2) 7 (13.5) 18 (34.6) 19 (40.4)

141 16 84 12 188 59 169 113 6 (25.0) 8 (33.3) 2 (8.3) 6 (25.0) 12 (50.0)

0.61 0.996 0.71 0.78 0.33 0.25 0.71 0.40 0.44

61.9 49.9 [27.3;45.0;87.8]

67.8 54.4 [29.0;45.0;100.5]

49.2 36.4 [19.8;43.0;61.0]

0.16

15 (19.7) 26.6 23.5 14 (20.3)

8 (15.4) 23.8 19.6 8 (16.7)

7 (29.2) 32.1 29.5 6 (28.6)

0.16 0.20 0.62

6 (14.0)

3 (9.7)

3 (25.0)

0.01

10 (14.7)

5 (10.9)

5 (22.7)

0.49

51 (67.1) 13 (17.1) 2 (2.6) 15 (19.7) 24 (31.6)

34 (65.4) 11 (21.2) 2 (3.8) 10 (19.2) 15 (28.8)

17 (70.8) 2 (8.3) 0 (0) 5 (20.8) 9 (37.5)

0.64 0.17 0.33 0.87 0.45

Data are provided as meanSD [25th, 50th, 75th percentile where appropriate]. P-values for comparison between smokers and non/ex-smokers. a Glomerular filtration rate was estimated using the MDRD2 formula. b All patients (n ¼ 71), non/ex-smokers (n ¼ 47), smokers (n ¼ 24). c All patients (n ¼ 69), non/ex-smokers (n ¼ 48), smokers (n ¼ 21). d All patients (n ¼ 43), non/ex-smokers (n ¼ 31), smokers (n ¼ 12). e All patients (n ¼ 68), non/ex-smokers (n ¼ 46), smokers (ss ¼ 22).

of transplantation and an exact quantification of post-transplant smoking is largely lacking. In the ALERT trial, smoking was a risk factor for graft loss in the unadjusted analysis (RR 2.33). In the adjusted analysis, it was a risk factor for the combined renal end points and death [10]. Sung reported a relative risk of 2.3 for graft loss in patients with pre-transplant smoking, of whom 90% continued smoking after transplantation [11]. Overall, smoking seems to more than double the risk for graft loss within 5–10 years. This is in line with the almost twice as high number of biopsied smokers with transplant failure compared with non-smokers. Having smoked more than 25 pack-years at time of transplantation was associated with a 30% increase in graft failure mainly due to patient death, more cardiovascular complications and invasive malignancies [12]. Another study identified smoking prior to transplantation as a risk factor for reduced patient survival [13]. In elderly patients smoking at the time of transplantation is associated with reduced patient and graft survival [14]. Interestingly, donor smoking also has a small but significant negative impact on both graft and recipient survival [15].

According to our data, the main target of smoking in a renal allograft seems to be the small arteries. Vascular fibrous intimal thickening was strongly associated with smoking after transplantation. This is even more remarkable, since the time between transplantation and biopsy in our patients was mostly in the range of 4–6 years and patients had smoked on average 3.1 pack-years during that period. This indicates that a relatively small dose of smoking may induce vascular changes rather rapidly in the renal allograft. The results after renal transplantation are in line with our observations in patients with primary glomerular disease, in whom we also found fibrointimal hyperplasia of small arteries in association with smoking [16]. The kidneys of these patients, however, were exposed to a far greater number of pack-years (on average 28) than were the grafts of the transplant patients. An additional effect of donor smoking cannot be excluded. Data from the United Network for Organ Sharing show a history of cigarette smoking in 42% of kidney donors [15]. Unfortunately, our study included no information on donor smoking habits. It seems unlikely, however, that kidneys of smokers were allocated only to


Serum creatinine (mg/dl) Glomerular filtration rate (ml/min/1.73m2)a Systolic blood pressure (mmHg) Diastolic blood pressure (mmHg) Total cholesterol (mg/dl) Triglycerides (mg/dl) Diabetes, n (%) Transplant failure, n (%) Living donor, n (%) Acute rejection, n (%) Donor age, above median (years), n (%)b Time period transplantation to biopsy (months) Cardiovascular event, n (%) Sclerotic glomeruli, (%) Arteriolar hyaline thickening ah3, n (%)c Vascular fibrous intimal thickening cv3, n (%)d Chronic/sclerosing allograft nephropathy Grade III, n (%)e Cyclosporin A, n (%) Tacrolimus, n (%) Sirolimus, n (%) Mycophenolic acid, n (%) Azathioprine, n (%)

All patients (n ¼ 76)

Smoking and chronic nephropathy

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Table 3. Association of different variables with glomerulosclerosis, arteriopathy, arteriolopathy and chronic sclerosing allograft nephropathy using linear regression analysis and ordinal logistic regression analysis (proportional odds models) Linear regression analysis: sclerotic glomeruli % Variable (increment) Adjusted B (95% CI)a Diabetes (1 ¼ yes, 2 ¼ no) 18.39(34.91– 1.87) Time since transplantation 1.55(0.50–3.60) (1 year) Body mass index (1 kg/m2) 1.22(2.73–0.30)

P-value 0.03 0.14 0.11

Proportional odds model: Arteriopathy (vascular fibrous intimal thickening cv0–3) Variable (increment) Current smoker (1 ¼ smoker, 0 ¼ non/ex-smoker)

Adjusted OR (95% CI)a P-value 4.45(1.60–12.40) 0.004

Proportional odds model: Arteriolopathy (arteriolar hyaline thickening ah0–3) Adjusted OR (95% CI)a P-value 1.29(1.17–1.43)